Flexible interconnects for modules of integrated circuits and methods of making and using the same

ABSTRACT

Flexible interconnects, flexible integrated circuit systems and devices, and methods of making and using flexible integrated circuitry are presented herein. A flexible integrated circuit system is disclosed which includes first and second discrete devices that are electrically connected by a discrete flexible interconnect. The first discrete devices includes a first flexible multi-layer integrated circuit (IC) package with a first electrical connection pad on an outer surface thereof. The second discrete device includes a second flexible multi-layer integrated circuit (IC) package with a second electrical connection pad on an outer surface thereof. The discrete flexible interconnect is attached to and electrically connects the first electrical connection pad of the first discrete device to the second electrical connection pad of the second discrete device.

CLAIM OF PRIORITY AND CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority to U.S. ProvisionalPatent Application No. 62/060,147, which was filed on Oct. 6, 2014, andis incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to printed circuit boards (PCB)and integrated circuits (IC). More particularly, aspects of thisdisclosure relate to bendable, stretchable and compressibleinterconnects for flexible integrated circuitry.

BACKGROUND

Integrated circuits (IC) are the cornerstone of the information age andthe foundation of today's information technology industries. Theintegrated circuit, a.k.a. “chip” or “microchip,” is a set ofinterconnected electronic components, such as transistors, capacitors,and resistors, which are etched or imprinted onto a tiny wafer ofsemiconducting material, such as silicon or germanium. Integratedcircuits take on various forms including, as some non-limiting examples,microprocessors, amplifiers, Flash memories, application specificintegrated circuits (ASICs), static random access memories (SRAMs),digital signal processors (DSPs), dynamic random access memories(DRAMs), erasable programmable read only memories (EPROMs), andprogrammable logic. Integrated circuits are used in innumerableproducts, including personal computers, laptop and tablet computers,smartphones, flat-screen televisions, medical instruments,telecommunication and networking equipment, airplanes, watercraft andautomobiles.

Advances in integrated circuit technology and microchip manufacturinghave led to a steady decrease in chip size and an increase in circuitdensity and circuit performance. The scale of semiconductor integrationhas advanced to the point where a single semiconductor chip can holdtens of millions to over a billion devices in a space smaller than aU.S. penny. Moreover, the width of each conducting line in a modernmicrochip can be made as small as a fraction of a nanometer. Theoperating speed and overall performance of a semiconductor chip (e.g.,clock speed and signal net switching speeds) has concomitantly increasedwith the level of integration. To keep pace with increases in on-chipcircuit switching frequency and circuit density, semiconductor packagescurrently offer higher pin counts, greater power dissipation, moreprotection, and higher speeds than packages of just a few years ago.

Conventional microchips are generally rigid structures that are notdesigned to be bent or stretched during normal operating conditions. Inaddition, IC's are typically mounted on a printed circuit board (PCB)that is as thick or thicker than the IC and similarly rigid. Processesusing thick and rigid printed circuit boards are generally incompatiblewith chips that are thinned or intended for applications requiringelasticity. Consequently, many schemes have been proposed for embeddingmicrochips on or in a flexible polymeric substrate. Flexible electroniccircuitry employing an elastic substrate material allows the IC to beadapted into innumerable shapes. This, in turn, enables many usefuldevice configurations not otherwise possible with rigid silicon-basedelectronic devices. However, some flexible electronic circuit designsare unable to sufficiently conform to their surroundings because theinterconnecting components are unable to flex in response toconformation changes. Such flexible circuit configurations are prone todamage, electronic degradation, and can be unreliable under rigorous usescenarios.

Many flexible circuits now employ stretchable and bendable interconnectsthat remain intact while the system stretches and bends. An“interconnect” in integrated circuits electrically couples the ICmodules to distribute clock and other signals and provide power/groundthroughout the electrical system. Some flexible interconnects capable ofbending and elasticity comprise metal segments that are embedded in anelastomer. For example, one known approach includes usingmicro-fabricated tortuous wires encased in a silicone elastomer toenable significant linear strain while maintaining conductivity.Elastically stretchable metal interconnects, however, tend to experiencean increase in resistance with mechanical strain. There is therefore acontinuing need for improved stretchable interconnects having improvedstretchability, electrical conductivity, and related properties forrapid and reliable manufacture of flexible electronic circuitry in avariety of different configurations.

SUMMARY

Disclosed herein are flexible interconnects for modules of integratedcircuits and methods of making and methods of using the same.Embodiments of this disclosure include stretchable interconnectfabrication between modules of ultrathin embedded Silicon IC die.Aspects of this disclosure are for “extremely stretchable” electricalinterconnects, flexible electronic circuitry using such extremelystretchable electrical interconnects, and methods of making and methodsof using the same. In at least some embodiments, methods are disclosedfor fabricating extremely stretchable integrated circuit electronicsthat are capable of stretching and compressing and bending whilewithstanding high translational strains, such as in the range of −100%to 100% and, in some embodiments, up to −100,000% to +100,000%, and/orhigh rotational strains, such as to an extent of 180° or greater, whilesubstantially maintaining electrical performance found in an unstrainedstate. Contrastingly, electronics fabricated from rigid single-crystalsemiconductor materials or other rigid substrate materials arecomparatively inflexible and brittle—many cannot withstand strains ofgreater than about +/−2%.

Conventional methods of manufacturing flexible electronic circuitsinvolve fabricating the interconnects in the material that is embeddingthe IC modules as a continuous single-piece structure. These existingprocesses are not always desirable because they: (1) waste material; (2)restrict the shape of the final package to maximize substrate realestate; (3) result in Loss of Yield and increased cost for each faultypart; (4) increase material costs; and (4) are relatively expensivemanufacturing processes. By way of contrast, embodiments of the presentdisclosure are directed to flexible multi-layer polymeric (e.g., silicon(Si)) interconnects that are fabricated separately from the IC islandsand subsequently attached or coupled to connection pads on outer (top)surfaces of adjacent IC islands. Embodiments of the present disclosureare also directed to metal interconnects (e.g., gold (Au) or copper (Cu)wirebonds) that are fabricated separately from the IC islands andsubsequently attached or coupled to connection pads on outer (top)surfaces of adjacent IC islands. Also disclosed are stretchableinterconnects fabricated from electrically conductive paste that arefabricated separately from the IC islands and subsequently attached orcoupled to connection pads on outer (top) surfaces of adjacent ICislands. Advantages of one or more of the disclosed configurations mayinclude reduction/elimination of wasted material, limited/norestrictions on the shape of the final package, minimal Loss of Yield,and reduced material costs and manufacturing costs.

Aspects of the present disclosure are directed to a flexible integratedcircuit system. The flexible integrated circuit system includes firstand second discrete devices. The first discrete device includes a firstflexible multi-layer integrated circuit (IC) package with a firstelectrical connection pad on a first outer surface thereof. In thisregard, the second discrete device includes a second flexiblemulti-layer integrated circuit (IC) package with a second electricalconnection pad on a second outer surface thereof. A discrete flexibleinterconnect is attached or coupled to and electrically connects thefirst electrical connection pad of the first discrete device to thesecond electrical connection pad of the second discrete device.

According to other aspects of the present disclosure, an extremelyflexible IC apparatus is presented. The IC apparatus comprises a firstflexible multi-layer integrated circuit (IC) package with a firstmicrochip embedded in or on a first flexible polymeric substrate, and afirst pair of adhesive layers, each of which is disposed on a respectiveside of the first flexible polymeric substrate. The first IC packagealso includes a first pair of conductive sheets, each of which isattached to the first flexible polymeric substrate by a respective oneof the first adhesive layers, and a first electrical connection padattached to an outer surface of one of the first conductive sheets. TheIC apparatus further comprises a second flexible multi-layer IC packagethat is separate and distinct from the first IC package. The second ICpackage includes a second microchip embedded in or on a second flexiblepolymeric substrate, and a second pair of adhesive layers, each of whichis disposed on a respective side of the second flexible polymericsubstrate. The second IC package also includes a second pair ofconductive sheets, each of which is attached to the second flexiblepolymeric substrate by a respective one of the second adhesive layers,and a second electrical connection pad attached to an outer surface ofone of the second conductive sheets. A flexible interconnect, which isseparate and distinct from the first and second IC packages,electrically connects the first electrical connection pad to the secondelectrical connection pad and mechanically couples the first flexiblemulti-layer IC package to the second flexible multi-layer IC package.

Other aspects of the present disclosure are directed to methods formaking and methods for using flexible integrated circuits. In oneaspect, the method includes: providing a first discrete device with afirst flexible multi-layer integrated circuit (IC) package including afirst outer surface with a first electrical connection pad; providing asecond discrete device with a second flexible multi-layer integratedcircuit (IC) package including a second outer surface with a secondelectrical connection pad; and, electrically connecting a discreteflexible interconnect to the first electrical connection pad of thefirst discrete device and the second electrical connection pad of thesecond discrete device.

For any of the disclosed configurations, the flexible interconnect maycomprise one or more pliant metal wires. Each of the pliant metal wiresmay comprise in-plane loops or out-of-plane-loops, or both, configuredto increase flexibility. For any of the disclosed configurations, theflexible interconnect may comprise a pliant multi-layer semiconductor.In this instance, the first flexible multi-layer IC package, the secondflexible multi-layer IC package, and the pliant multi-layersemiconductor of the flexible interconnect all comprise common layers ofmaterials, according to some embodiments. For any of the disclosedconfigurations, the flexible interconnect may comprise a conductivesubstrate fabricated from an electrically conductive paste. In thisinstance, the flexible interconnect may comprise a web of metallicinterconnects printed onto the substrate. One or more or all of thedisclosed configurations may be implemented as an “extremelystretchable” IC device.

The above summary is not intended to represent each embodiment or everyaspect of the present disclosure. Rather, the foregoing summary merelyprovides an exemplification of some of the novel aspects and featuresset forth herein. The above features and advantages, and other featuresand advantages of the present disclosure, will be readily apparent fromthe following detailed description of representative embodiments andmodes for carrying out the present invention when taken in connectionwith the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective-view illustration of an example of a flexibleelectronic circuit system with integrated circuit (IC) packagesconnected by pliant wirebonded interconnects in accord with aspects ofthe present disclosure.

FIG. 2 is a cross-sectional side-view illustration of a representativeflexible electronic circuit system with a plurality of multi-layer ICmodules connected by pliant wirebonded interconnects in accord withaspects of the present disclosure.

FIG. 3 is a cross-sectional side-view illustration of a representativeflexible electronic circuit system with a plurality of multi-layer ICmodules connected by pliant multi-layer polymeric interconnects inaccord with aspects of the present disclosure.

FIG. 4 is a cross-sectional side-view illustration of a representativeflexible electronic circuit system with a plurality of multi-layer ICmodules connected by pliant conductive-paste interconnects in accordwith aspects of the present disclosure.

FIG. 5 is a process and assembly flow diagram for fabricating a flexibleintegrated circuit system in accord with aspects of the presentdisclosure.

The present disclosure is susceptible to various modifications andalternative forms, and some representative embodiments have been shownby way of example in the drawings and will be described in detailherein. It should be understood, however, that the invention is notintended to be limited to the particular forms disclosed. Rather, thedisclosure is to cover all modifications, equivalents, combinations,subcombinations, and alternatives falling within the spirit and scope ofthe invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

This disclosure is susceptible of embodiment in many different forms.There are shown in the drawings, and will herein be described in detail,representative embodiments with the understanding that the presentdisclosure is to be considered as an exemplification of the principlesof the present disclosure and is not intended to limit the broad aspectsof the disclosure to the embodiments illustrated. To that extent,elements and limitations that are disclosed, for example, in theAbstract, Summary, and Detailed Description sections, but not explicitlyset forth in the claims, should not be incorporated into the claims,singly or collectively, by implication, inference or otherwise. Forpurposes of the present detailed description, unless specificallydisclaimed or logically prohibited: the singular includes the plural andvice versa; and the word “including” or “comprising” or “having” means“including without limitation.” Moreover, words of approximation, suchas “about,” “almost,” “substantially,” “approximately,” and the like,can be used herein in the sense of “at, near, or nearly at,” or “within3-5% of,” or “within acceptable manufacturing tolerances,” or anylogical combination thereof, for example.

The terms “flexible” and “stretchable” and “bendable,” including rootsand derivatives thereof, when used as an adjective to modify electricalcircuitry, electrical systems, and electrical devices or apparatuses,are meant to encompass electronics that comprise at least somecomponents having pliant or elastic properties such that the circuit iscapable of being flexed, stretched and/or bent, respectively, withouttearing or breaking or compromising their electrical characteristics.These terms are also meant to encompass circuitry having components(whether or not the components themselves are individually stretchable,flexible or bendable) that are configured in such a way so as toaccommodate and remain functional when applied to a stretchable,bendable, inflatable, or otherwise pliant surface. In configurationsdeemed “extremely stretchable,” the circuitry is capable of stretchingand/or compressing and/or bending while withstanding high translationalstrains, such as in the range of −100% to 100% and, in some embodiments,up to −100,000% to +100,000%, and/or high rotational strains, such as toan extent of 180° or greater, without fracturing or breaking and whilesubstantially maintaining electrical performance found in an unstrainedstate.

The discrete “islands” or “packages” mentioned herein are discreteoperative devices, e.g., arranged in a “device island” arrangement, andare themselves capable of performing the functionality described herein,or portions thereof. Such functionality of the operative devices caninclude, for example, integrated circuits, physical sensors (e.g.temperature, pH, light, radiation, etc.), biological sensors, chemicalsensors, amplifiers, A/D and D/A converters, optical collectors,electro-mechanical transducers, piezoelectric actuators, light emittingelectronics (e.g., LEDs), and any combination thereof. A purpose and anadvantage of using one or more standard ICs (e.g., CMOS on singlecrystal silicon) is to use high-quality, high-performance, andhigh-functioning circuit components that are readily accessible andmass-produced with well-known processes, and which provide a range offunctionality and generation of data far superior to that produced bypassive means. The discrete islands may range from about, but notlimited to, 10-100 micrometers (μm) in size measured on an edge or bydiameter.

Referring now to the drawings, wherein like reference numerals refer tolike components throughout the several views, FIG. 1 illustrates anexample of a flexible integrated circuit (IC) system, designatedgenerally as 10, which may be adapted as or integrated into an“extremely stretchable” IC apparatus. Many of the disclosed concepts arediscussed with reference to the representative systems depicted in thedrawings; the systems illustrated herein, however, are provided merelyas exemplary applications by which the various inventive aspects andfeatures of this disclosure can be applied. Thus, the novel aspects andfeatures of the present disclosure are not per se limited to theparticular arrangements and components presented in the drawings.Moreover, only selected components of the system(s) have been shown andwill be described in additional detail hereinbelow. Nevertheless, thesystems and devices discussed herein can include numerous additional andalternative features, and other well-known peripheral components, forexample, for carrying out the various methods and functions disclosedherein. Some of the illustrated components are optional and, thus, canbe removed.

The flexible IC system 10 of FIG. 1 comprises various electroniccomponents (collectively referred to as “circuitry”), such as alaminated battery 12, a set of microchips 14, a sensor 16, a sensor hub18, antenna 20, and an assortment of integrated passive devices (IPD)22A, 22B and 22C. The circuitry is applied, secured, embedded orotherwise affixed to substrate 24, which is flexible—e.g., stretchable,bendable and/or compressible—as described herein. As such, the substrate24 can be made of a plastic material or an elastomeric material, orcombinations thereof. Examples of suitable flexible elastomers for theIC substrate material include polymeric organosilicon compounds(commonly referred to as “silicones”), including Polydimethylsiloxane(PDMS). Other non-limiting examples of materials suitable for thesubstrate 24 include polyimide, photopatternable silicon, SU8 polymer,PDS polydustrene, parylene and its derivatives and copolymers(parylene-N), ultrahigh molecular weight polyethylene, polyether etherketones (PEEK), polyurethanes, polylactic acid, polyglycolic acid,polymer composites, silicones/siloxanes, polytetrafluoroethylene,polyamic acid, polymethyl acrylate, and combinations thereof. Thesubstrate 24 can take on any possible number of shapes, sizes, andconfigurations. In the illustrated example, the substrate issubstantially flat and, in some embodiments, configured to be anelongated sheet or strip.

The circuitry of FIG. 1 comprises one or more sensors 16 (also termed“sensor devices”) to detect any of various parameters. These parameterscan include, in any combination, thermal parameters (e.g., temperature),optical parameters (e.g., infrared energy), electrochemical andbiochemical parameters, such as pH, enzymatic activity, blood components(e.g., glucose), ion concentrations, and protein concentrations,electrical parameters (e.g., resistance, conductivity, impedance, etc.),acoustic parameters, tactile parameters (e.g., pressure, surfacecharacteristics, or other topographic features), etc. In this regard,one or more of the sensors 16 may be a thermocouple, a silicon band gaptemperature sensor, a thin-film resistance temperature device, an LEDemitter, a photodetector, a piezoelectric sensor, an ultrasonic sensor,an ion sensitive field effect transistor, etc. For some implementations,one or more of the sensors 16 can be coupled to a differential amplifierand/or a buffer and/or an analog to digital converter. The sensor hub18, which may be in the nature of a microcontroller or digital signalprocessor (DSP), operates to integrate data signals from the sensor(s)16 and process such signals. Signals from the sensor(s) 16 can beprocessed using multiplexing techniques, and can be switched into andprocessed by one or a few amplifier/logic circuits, including one ormore of the microchips 14.

Battery 12 acts as a power source to supply power to the circuitry inthe flexible IC system 10 of FIG. 1. Any suitable battery which is smallin size and has a sufficiently long life with a suitable amp-hourcapacity may be employed. It is also within the scope of this disclosureto employ alternative means for powering the system 10, includingexternal power supplies. According to some embodiments, the flexible ICsystem 10 also includes a data transmission facility with an RF antenna20 to wirelessly communicate with external devices. The antenna 20 cantake on various forms, including a printed trace antenna coil with vias,which may be operable as a low frequency, high frequency or ultra-highfrequency antenna. Other forms of wired and wireless signal transmissionare also within the scope of this disclosure. Each integrated passivedevice (IPD) 22A-22C may comprise, as some non-limiting examples, afilter, a transformer, a photodiode, LED, TUFT, electrode,semiconductor, duplexer, coupler, phase shifter, thin-film device,circuit element, control elements, capacitors, resistors, inductors,buffer or other passive component. IPD's 22A-22C can be fabricated asstandalone devices each having a silicon chip that may be connected toan active integrated circuit (e.g., a microprocessor).

For embodiments where the substrate 24 is stretchable or compressible,the illustrated circuitry is configured in applicable manners, such asthose described herein, to be stretchable or compressible and/or toaccommodate such stretching/compressing of the substrate 24. Similarly,for embodiments where the substrate 24 is bendable, but not necessarilystretchable, the illustrated circuitry is configured in applicablemanners, such as those described herein, to be bendable and/oraccommodate such bending of the substrate. For example, each of theillustrated modules or “islands” is connected to one or more adjacentmodules with flexible wirebonded interconnects, some of which aredesignated generally as 26 in FIG. 1. The connection point of theindividual interconnects to a device island may be anywhere along thedevice island edge, or may be at a point on the top surface of thedevice island (i.e., the surface opposite the substrate 24). The bondwires 26 are attached to externally mounted bond pads 28 on the modulesand extend to a corresponding externally mounted bond pad 28 on anadjacent module. The bond wires can be attached through any knownwirebonding technique, such as: ultrasonic bonding which uses acombination of pressure and ultrasonic vibration bursts to form ametallurgical cold weld; thermocompression bonding which uses acombination of pressure and elevated temperature to form a weld; andthermosonic bonding which uses a combination of pressure, elevatedtemperature, and ultrasonic vibration bursts to form a weld joint.

Turning next to FIG. 2, there is shown a cross-sectional illustration ofa representative flexible electronic circuit system, designatedgenerally as 100, with multi-layer IC modules connected via pliantwirebonded interconnects. While differing in appearance, the flexible ICsystem 100 of FIG. 2 can take on any of the various forms, optionalconfigurations, and functional alternatives described herein withrespect to the examples shown in FIGS. 1 and 3-5, and thus can includeany of the corresponding options and features. Like the system 10 ofFIG. 1, for example, the system 100 of FIG. 2 may be configured as anultrathin, extremely stretchable integrated circuit system. Moreover,system 100 comprises an assortment of discrete devices—e.g., first,second and third discrete devices 102A, 102B and 102C—that are arrangedin a “device island” arrangement and electrically coupled by pliantwirebonded interconnects. It is contemplated that the system 100comprise greater or fewer than the three discrete devices shown in FIG.2, each of which may take on alternative forms and configurations.

In the embodiment of FIG. 2, each of the discrete devices 102A-102Cincludes a flexible multi-layer integrated circuit (IC) package capableof performing one or more of the functions described herein. Themulti-layer IC package of each discrete device, for example, includes arespective microchip—first, second and third microchips 104A, 104B and104C—embedded in or on a respective flexible polymeric substrate—first,second and third substrates 106A, 106B and 106C. The polymericsubstrates 106A-106C may be fabricated in any industry-recognized mannerand from any of the materials described above with respect to thesubstrate 24 of FIG. 1. Optionally, the substrates 106A-106C may befabricated from a liquid crystal polymer or a polyimide polymer, such asKAPTON® film available from DuPont™. The polymeric substrate can have athickness of about 60 μm to about 85 μm or, in some embodiments, about25 μm to about 50 μm or, in some embodiments, about 7 μm to about 10 μm.Each substrate may also comprise a layer of a flexible polymer disposedon a layer of conductive material, such as copper, gold, aluminum, orsome combination thereof. In an example, PCB metal layers can bepatterned on opposing sides of the polymeric substrate 106A-106C.

One or more or all of the microchips 104A-104C may be a “thin chip”configuration with a thickness of about 2-7 μm or, in some embodiments,a thickness of about 5-7 μm or, in some embodiments, a thickness ofabout 3-5 μm or, in some embodiments, a thickness of about 2-3 μm. Inthe representative systems, methods and devices described herein, eachthin chip can be one or more passive electronic devices and/or one ormore active electronic devices. By comparison, a thin chip may befabricated onto a silicon-based semiconductor die 104 with a thicknessof approximately 35-50 μm or, in some embodiments, a thickness ofapproximately 15-25 μm or, in some embodiments, a thickness ofapproximately 10-15 μm, for example. Non-limiting examples of devicesthat can be embedded according to any of the principles described hereininclude an amplifier, a transistor, a photodiode array, a photodetector,a sensor, a light-emitting device, a photovoltaic device, asemiconductor laser array, an optical imaging device, a logic gatearray, a microprocessor, an opto-electronic device, amicroelectromechanical device, a microfluidic device, ananoelectromechanical device, a thermal device, or other devicestructures.

A pair of adhesive layers is disposed on opposing sides of the flexiblepolymeric substrates 106A-106C of the multi-layer IC package of eachdiscrete device 102A-102C. In an example, the first flexible multi-layerIC package includes a first pair of adhesive layers 108A, each of whichis attached to a respective side of the first polymeric substrate 106A.Likewise, the second flexible multi-layer IC package includes a secondpair of adhesive layers 108B, each of which is attached to a respectiveside of the second polymeric substrate 106B. In addition, the thirdmulti-layer IC package includes a third pair of adhesive layers 108C,each of which is attached to a respective side of the third polymericsubstrate 106C. Each layer of adhesive can have a thickness of about 8μm to about 35 μm or, in some embodiments, about 20 μm to about 35 μmor, in some embodiments, about 12 μm to about 15 μm or, in someembodiments, about 8 μm to about 10 μm. The adhesive can be a conductiveadhesive or a non-conductive (dielectric) adhesive that is configured towithstand the temperatures of further processing. Conductive adhesivecan be used to establish electrical communication between the conductivematerial of the substrate and conductive contact pads on the top surfaceof the thin chip. In an example, the adhesive layers 108A-108C can be afluropolymer adhesive, a polyimide (PI) adhesive, an epoxy adhesive, oran acrylic adhesive, such as PYRALUX® Bond-Ply available from DuPont™Optionally, the material of adhesive layer can be selected such that itis a non-conductive electrical insulator capable of adhering theadjacent layers. Each multi-layer IC package may optionally includeadditional adhesive layers, as represented in FIG. 2 by the additionalpair of adhesive layers 108D attached to the outer surfaces of the firstadhesive layers 108A. With the additional layers, the total thickness ofthe adhesive may be as large as 85 μm, according to some embodiments.

As illustrated in FIG. 2, the flexible multi-layer IC package of eachdiscrete device 102A-102C further comprises a pair of electricallyconductive (polymeric or metallic) layers on opposing sides of theflexible polymeric substrates 106A-106C. For example, the first flexiblemulti-layer IC package includes a first pair of metallic sheets 110Aattached via the first adhesive layers 108A to the first flexiblepolymeric substrate 106A. Likewise, the second multi-layer IC packageincludes a second pair of metallic sheets 110B attached via the secondadhesive layers 108B to the second flexible polymeric substrate 106B. Inaddition, the third multi-layer IC package includes a third pair ofmetallic sheets 110C attached via the third adhesive layers 108C to thethird flexible polymeric substrate 106C. Each metallic sheet can have athickness of about 5 μm to about 20 μm or, in some embodiments, about 15μm to about 20 μm or, in some embodiments, about 10 μm to about 12 μmor, in some embodiments, about 5 μm to about 8 μm. Electricallyconductive metallic layers can be fabricated, for example, from copperor aluminum or a combination thereof.

One or more vias can be generated as channels (e.g., with a laser drill)extending through outer layers of each flexible multi-layer IC packageto allow for conductive connections between different layers of themulti-layer stack. In FIG. 2, for example, the first multi-layer ICpackage includes a first pair of vias 112A that extend through a (top)conductive sheet 110A and corresponding (top) adhesive layer 108A to thefirst microchip 104A. In the same vein, the second multi-layer ICpackage includes a second pair of vias 112B that extend through a (top)conductive sheet 110B and corresponding (top) adhesive layer 108B to thesecond microchip 104B. Likewise, the third multi-layer IC packageincludes a third pair of vias 112C that extend through a (top)conductive sheet 110C and corresponding (top) adhesive layer 108C to thesecond microchip 104C. Once these vias have been created, the vias canbe electroplated or filled through sputtering or other known techniqueto create electrical connections from the top conductive layer to anelectrical contact pad of the chip. The conductive layers can then bepatterned and an overlay can be applied to the outer surface of eachconductive layer. In some implementations, the overlay is non-conductivepolymer.

On the outer surface of each discrete device 102A-102C are one or moreelectrical connection pads 114A, 114B and 114C, respectively, forelectrically coupling with adjacent devices. By way of non-limitingexample, the first discrete device 102A is shown with two electricalconnection pads 114A on the top surface of the first multi-layer ICpackage to provide electrical communication with the first microchip104A, while the second discrete device 102B is shown with two electricalconnection pads 114B on the top surface of the second multi-layer ICpackage to provide electrical communication with the second microchip104B. Similarly, the third discrete device 102C is shown with at leastone electrical connection pad 114C on the top surface of the thirdmulti-layer IC package to provide electrical communication with thethird microchip 104C. Optionally, the first discrete device 102Aincludes a corresponding set of surface-mount-technology (SMT)components 118A mounted on the first outer surface of the first flexiblemulti-layer IC package, and the second discrete device 102B includes asecond set of SMT components 118B mounted on the outer surface of thesecond flexible multi-layer IC package.

It is contemplated that one or more or all of the illustratedmulti-layer IC packages comprise additional or fewer layers than thesandwich constructions shown in FIG. 2. It should also be noted that theuse of the term “layer” in the description and claims does notnecessarily require that particular segment of the sandwich constructionbe continuous or span the entirety of (i.e., be coextensive with) allremaining layers unless otherwise explicitly stated in the claims. Whilepreferable in some applications, it is not necessary in practice thatthe adhesive layers of each package be fabricated from the same materialand the conductive layers be fabricated from the same material.Moreover, the individual packages may be vacuum laminated as discrete,unitary structures prior to electrical coupling with one or moreadjacent devices.

Discrete flexible interconnects are attached to and electrically connectthe electrical connection pad of one discrete device to the electricalconnection pad of another discrete device. In accord with the flexibleIC system 100 of FIG. 2, a discrete flexible interconnect in the form ofa curvilinear wirebond 120AB is attached or coupled to and electricallyconnects a first (right) electrical connection pad 114A of the firstdiscrete device 102A to a second (left) electrical connection pad 114Bof the second discrete device 102B. Likewise, a discrete flexibleinterconnect in the form of a curvilinear wirebond 120AC is attached orcoupled to and electrically connects a first (left) electricalconnection pad 114A of the first discrete device 102A to a third (right)electrical connection pad 114C of the third discrete device 102C. In theillustrated example, the flexible interconnects each comprise one ormore pliant metal wires, e.g., made from copper or gold with a circularcross-section, each of which may comprise in-plane loops (one of whichcan be seen to the far right in FIG. 2) or out-of-plane-loops, or both,that increase the elasticity of the wire. Examples of such in-planeloops and out-of-plane-loops are depicted and described in commonlyowned U.S. Pat. No. 8,536,667, which is incorporated herein by referencein its entirety and for all purposes. Any in-plane or out-of-plane loopshelp to ensure a sufficient degree of stretchability and flexibility.These wirebonded interconnects are fabricated separately from andsubsequently attached to the discrete flexible IC modules (e.g., usingthermosonic wirebonding techniques). Proper solder joints and welds arecreated to attach the interconnects to the externally mounted pads andthereby ensure reliability of the interconnects.

FIG. 3 illustrates another representative flexible electronic circuitsystem, designated generally as 200, with multi-layer IC modules thatare connected via pliant multi-layer polymeric interconnects. Likereference numerals are used in FIGS. 3 and 4 to indicate similarstructure from FIG. 2. For example, the system 200 of FIG. 3 and thesystem 300 of FIG. 4 each comprises a similar assortment of discretedevices—e.g., first, second and third discrete devices 102A, 102B and102C—that are arranged in a “device island” arrangement and electricallycoupled by pliant electrical interconnects. Moreover, the flexible ICsystems 200 and 300 can take on any of the various forms, optionalconfigurations, and functional alternatives described herein withrespect to the other examples shown in the figures, and vice versa,unless explicitly or logically prohibited.

Discrete flexible interconnects mechanically attach to and electricallyconnect the electrical connection pads of one discrete device to theelectrical connection pads of other discrete devices in FIG. 3. The topside of each module 102A-102C is provided with a connection pad 114A,114B, 114C for electrically connecting to other packages. According tothe illustrated example, a first discrete flexible interconnect in theform of a pliant multi-layer semiconductor 220AB is attached or coupledto and electrically connects a first (right) electrical connection pad114A of the first discrete device 102A to a second (left) electricalconnection pad 114B of the second discrete device 102B. Likewise, asecond discrete flexible interconnect in the form of a pliantmulti-layer semiconductor 220AC is attached to and electrically connectsa first (left) electrical connection pad 114A of the first discretedevice 102A to a third (right) electrical connection pad 114C of thethird discrete device 102C. According to some embodiments, the firstdiscrete flexible interconnect in the form of a pliant multi-layersemiconductor 220AB and the second discrete flexible interconnect in theform of a pliant multi-layer semiconductor 220AC are attached torespective electrical connection pads 114A, 114B, 114C using atraditional solder attach.

The discrete flexible IC modules 102A-102C are built as separatepackages with the IC embedded in the substrate. Interconnects 220AB,220AC are manufactured in separate PCB flex substrates from the ICmodules 102A-102C, and can be cut with a serpentine or other non-linearshape to provide stretchability. Examples of interconnects withserpentine shapes are depicted and described in U.S. Pat. Nos. 8,389,862and 8,729,524, both of which are incorporated herein by reference intheir respective entireties and for all purposes. The top side of eachmodule 102A-102C is provided with a connection pad 114A, 114B, 114C forelectrically connecting to other packages. Any SMT components requiredfor a particular IC can be mounted on the top surface of the package. Itis possible to stack flexible modules on top of each other similar toPackage-on-Package (PoP) technology using appropriate solder, etc.Examples of semiconductor devices having package-on-package (POP)configurations are disclosed in U.S. Pat. Nos. 7,696,618 and 7,250,675,both of which are incorporated herein by reference in their respectiveentireties. In so doing, the input-output connection points (I/Os) foreach package can be minimized so as to restrict the number of requiredinterconnections.

The flexible multi-layer IC package of the first discrete device 102A,the flexible multi-layer IC package of the second discrete device 102B,and the multi-layer semiconductors of each flexible interconnect 220AB,220AC may all comprise common layers of materials, according to someembodiments. For instance, according to some embodiments, eachinterconnect 220AB, 220AC comprises a polymeric substrate 206A and 206B,respectively, that may be fabricated from a liquid crystal polymer or apolyimide polymer, such as KAPTON® film. According to some embodiments,the flexible interconnects 220AB, 220AC further comprise a pair ofelectrically conductive (polymeric or metallic) layers 210A and 210B,respectively, on opposing sides of the flexible polymeric substrates206A, 206B. These electrically conductive layers can be fabricated, forexample, from copper or aluminum or a combination thereof. First andsecond pairs of adhesive layers 208A and 208B are disposed on opposingsides of the flexible polymeric substrates 206A, 206B, respectively,covering one of the conductive layers 210A, 210B. Similar to theadhesive layers 108A-108C of the discrete devices 102A-102C, theadhesive layers 208A, 208B of the flexible interconnects 220AB, 220ACcan be a fluropolymer adhesive, a polyimide (PI) adhesive, an epoxyadhesive, or an acrylic adhesive, such as PYRALUX® Bond-Ply.

FIG. 4 illustrates yet another representative flexible electroniccircuit system, designated generally as 300, this time utilizing pliantconductive-paste-based interconnects to connect the discrete multi-layerIC modules. According to the illustrated example, a first discreteflexible interconnect in the form of a conductive substrate fabricatedfrom an electrically conductive paste 320AB is attached or coupled toand electrically connects a first (right) electrical connection pad 114Aof the first discrete device 102A to a second (left) electricalconnection pad 114B of the second discrete device 102B. Likewise, asecond discrete flexible interconnect in the form of a conductivesubstrate fabricated from an electrically conductive paste 320AC isattached or coupled to and electrically connects a first (left)electrical connection pad 114A of the first discrete device 102A to athird (right) electrical connection pad 114C of the third discretedevice 102C. Each flexible interconnect 320AB, 320AC may comprise a webof metallic interconnects (e.g., copper or gold or a conductive polymeror paste) that printed or otherwise patterned, for example, using screenprint or ink jet printing techniques onto the substrate.

FIG. 5 illustrates a representative method 400 for manufacturingflexible integrated circuits. This method will be described withreference to the various configurations and features shown in FIGS. 1through 4 of the drawings; such reference is being provided purely byway of explanation and clarification. At block 401, the method 400includes embedding a thin die in large panels, punching out known goodflexible parts or “KGFP,” and sorting into waffle trays. Thus, theindividual circuits can be tested before being punched out therebyreducing the potential for distributing malfunctioning parts. Next, themethod 400 includes picking and placing the flex packages (e.g., theKGFP's are identified and sorted while any malfunctioning circuits areleft) onto temporary rigid substrates (reusable substrate withdisposable adhesive), as indicated at block 403. The adhesive strengthcan be modulated by light and/or heat. At block 405, wirebond flexpackage assemblies are placed on rigid substrates as a temporary carrierfor copper wirebonding. The method 400 proceeds to block 407 toencapsulate the top side of the devices and remove the temporarysubstrate from the bottom. Block 409 includes encapsulating the bottomside of the devices and die cutting.

Also presented herein is a method for assembling flexible integratedcircuits. This method includes, in any logical order and any logicalcombination: providing a first discrete device with a first flexiblemulti-layer integrated circuit (IC) package including a first outersurface with a first electrical connection pad; providing a seconddiscrete device with a second flexible multi-layer integrated circuit(IC) package including a second outer surface with a second electricalconnection pad; and electrically connecting a discrete flexibleinterconnect to the first electrical connection pad of the firstdiscrete device and the second electrical connection pad of the seconddiscrete device. The flexible interconnect may comprise one or morepliant metal wires. Optionally or alternatively, the flexibleinterconnect comprises a pliant multi-layer semiconductor or aconductive substrate fabricated from an electrically conductive paste.The first multi-layer IC package may comprise a first microchip embeddedin or on a first flexible polymeric substrate, a first adhesive layer onthe first flexible polymeric substrate, and a first conductive sheetattached to the first flexible polymeric substrate by the first adhesivelayer. Likewise, the second flexible multi-layer IC package may comprisea second microchip embedded in or on a second flexible polymericsubstrate, a second adhesive layer on the second flexible polymericsubstrate, and a second conductive sheet attached to the second flexiblepolymeric substrate by the first adhesive layer.

In some embodiments, the aforementioned methods each includes at leastthose steps shown in FIG. 5 and/or those steps enumerated above. It isalso within the scope and spirit of the present disclosure to omitsteps, include additional steps, and/or modify the order presentedherein. It should be further noted that each of the foregoing methodscan be representative of a single sequence of related steps; however, itis expected that each of these methods will be practiced in a systematicand repetitive manner.

The present disclosure is not limited to the precise construction andcompositions disclosed herein; any and all modifications, changes, andvariations apparent from the foregoing descriptions are within thespirit and scope of the disclosure as defined in the appended claims.Moreover, the present concepts expressly include any and allcombinations and subcombinations of the preceding elements and aspects.

What is claimed:
 1. A flexible integrated circuit system comprising: afirst discrete device with a first flexible multi-layer integratedcircuit (IC) package including a first outer surface with a firstelectrical connection pad; a second discrete device with a secondflexible multi-layer integrated circuit (IC) package including a secondouter surface with a second electrical connection pad; and a discreteflexible interconnect attached to and electrically connecting the firstelectrical connection pad of the first discrete device to the secondelectrical connection pad of the second discrete device.
 2. The flexibleintegrated circuit system of claim 1, wherein the flexible interconnectcomprises one or more pliant metal wires.
 3. The flexible integratedcircuit system of claim 2, wherein the one or more pliant metal wirescomprise in-plane loops or out-of-plane-loops, or both, configured toincrease flexibility.
 4. The flexible integrated circuit system of claim1, wherein the flexible interconnect comprises a pliant multi-layersemiconductor.
 5. The flexible integrated circuit system of claim 4,wherein the first flexible multi-layer IC package, the second flexiblemulti-layer IC package, and the pliant multi-layer semiconductor of theflexible interconnect all comprise common layers of materials.
 6. Theflexible integrated circuit system of claim 1, wherein the flexibleinterconnect includes a conductive substrate fabricated from anelectrically conductive paste.
 7. The flexible integrated circuit systemof claim 6, wherein the flexible interconnect comprises a web ofmetallic interconnects printed onto the substrate.
 8. The flexibleintegrated circuit system of claim 1, wherein the first flexiblemulti-layer IC package comprises a first microchip embedded in or on afirst flexible polymeric substrate, and the second flexible multi-layerIC package comprises a second microchip embedded in or on a secondflexible polymeric substrate.
 9. The flexible integrated circuit systemof claim 8, wherein the first flexible multi-layer IC package furthercomprises a first adhesive layer on the first flexible polymericsubstrate, and the second flexible multi-layer IC package furthercomprises a second adhesive layer on the second flexible polymericsubstrate.
 10. The flexible integrated circuit system of claim 9,wherein the first flexible multi-layer IC package further comprises afirst conductive layer coupled via the first adhesive layer to the firstflexible polymeric substrate, and the second flexible multi-layer ICpackage further comprises a second conductive layer coupled via thesecond adhesive layer to the second flexible polymeric substrate. 11.The flexible integrated circuit system of claim 10, wherein the firstflexible multi-layer IC package further comprises a first via extendingthrough the first conductive layer and the first adhesive layer to thefirst microchip, and the second flexible multi-layer IC package furthercomprises a second via extending through the second conductive layer andthe second adhesive layer to the second microchip.
 12. The flexibleintegrated circuit system of claim 1, wherein the first flexiblemulti-layer IC package includes a first set of surface-mount-technology(SMT) components mounted on the first outer surface, and the secondflexible multi-layer IC package includes a second set of SMT componentsmounted on the second outer surface.
 13. The flexible integrated circuitsystem of claim 1, wherein the flexible interconnect maintainssubstantially identical electrical conductivity when stretched up toapproximately 100% or bent up to approximately 180 degrees, or both. 14.An extremely flexible integrated circuit apparatus comprising: a firstflexible multi-layer integrated circuit (IC) package including: a firstflexible polymeric substrate; a first microchip embedded in or on thefirst flexible polymeric substrate; a first pair of adhesive layers,each on a respective side of the first flexible polymeric substrate; afirst pair of conductive sheets, each coupled to the first flexiblepolymeric substrate by a respective one of the first adhesive layers;and a first electrical connection pad attached or coupled to an outersurface of one of the first conductive sheets; a second flexiblemulti-layer integrated circuit (IC) package, which is separate anddistinct from the first flexible multi-later IC package, including: asecond flexible polymeric substrate; a second microchip embedded in oron the second flexible polymeric substrate; a second pair of adhesivelayers, each on a respective side of the second flexible polymericsubstrate; a second pair of conductive sheets, each coupled to thesecond flexible polymeric substrate by a respective one of the secondadhesive layers; and a second electrical connection pad attached orcoupled to an outer surface of one of the second conductive sheets; anda flexible interconnect separate and distinct from the first and secondflexible multi-layer IC packages, the flexible interconnect electricallyconnecting the first electrical connection pad to the second electricalconnection pad.
 15. A method for assembling flexible integratedcircuits, the method comprising: providing a first discrete device witha first flexible multi-layer integrated circuit (IC) package including afirst outer surface with a first electrical connection pad; providing asecond discrete device with a second flexible multi-layer integratedcircuit (IC) package including a second outer surface with a secondelectrical connection pad; and electrically connecting a discreteflexible interconnect to the first electrical connection pad of thefirst discrete device and the second electrical connection pad of thesecond discrete device.
 16. The method of claim 15, wherein the flexibleinterconnect comprises one or more pliant metal wires.
 17. The method ofclaim 15, wherein the flexible interconnect comprises a pliantmulti-layer semiconductor.
 18. The method of claim 15, wherein theflexible interconnect includes a conductive substrate fabricated from anelectrically conductive paste.
 19. The method of claim 15, wherein thefirst flexible multi-layer IC package comprises a first flexiblepolymeric substrate, a first microchip embedded in or on the firstflexible polymeric substrate, a first adhesive layer on the firstflexible polymeric substrate, and a first conductive sheet attached tothe first flexible polymeric substrate by the first adhesive layer. 20.The method of claim 19, wherein the second flexible multi-layer ICpackage comprises a second flexible polymeric substrate, a secondmicrochip embedded in or on the second flexible polymeric substrate, asecond adhesive layer on the second flexible polymeric substrate, and asecond conductive sheet attached to the second flexible polymericsubstrate by the first adhesive layer.